1. Field of the Invention
The present invention relates to a wire electrical discharge machine, a machining path generator of a wire electrical discharge machine, and a machining method for use in a wire electrical discharge machine for performing path compensation in a concave arc corner portion.
2. Description of the Related Art
FIG. 13 is a schematic block diagram of a conventional machining path generator configured to generate a machining path in a wire electrical discharge machine.
Machining program storage means 11 stores a large number of machining programs needed for machining. Machining program analysis means 12 analyzes a machining program specified by an operator or the like, extracts data concerning a programmed path, and transmits the extracted data to programmed path generation means 14. The machining program analysis means 12 also gives an instruction on a needed offset amount to offset amount storage means 13 based on a command code concerning an offset amount in the machining program. The offset amount storage means 13 stores a large number of wire offset amounts needed for machining. The offset amount storage means 13 selects an offset amount needed for machining for each cutting pass as instructed by the machining program analysis means 12, and transmits the offset amount to machining path generation means 15. The programmed path generation means 14 receives data concerning a programmed path from the machining program analysis means 12, and generates a programmed path. The machining path generation means 15 receives the data concerning a programmed path from the programmed path generation means 14 and the offset amount from the offset amount storage means 13, and, based on these pieces of information, generates a machining path along which a wire actually moves.
Each machining program is stored in the machining program storage means 11 by an operator in advance. Moreover, each offset amount is also set by an operator in advance and stored in the offset amount storage means 13. When an operator selects a needed machining program from the machining program storage means 11, the selected machining program is transmitted from the machining program storage means 11 to the machining program analysis means 12. The machining program analysis means 12 analyzes the machining program transmitted from the machining program storage means 11, extracts data concerning a programmed path from the machining program, and transmits the extracted data to the programmed path generation means 14. Moreover, the machining program analysis means 12 gives an instruction on a needed offset amount to the offset amount storage means 13 based on a command code concerning an offset amount.
The programmed path generation means 14 receives the data concerning a programmed path from the machining program analysis means 12, generates a programmed path based on the received data, and transmits the programmed path to the machining path generation means 15. The offset amount storage means 13 selects an offset amount as instructed by the machining program analysis means 12, and transmits the offset amount to the machining path generation means 15. The machining path generation means 15 receives data concerning a programmed path from the programmed path generation means 14 and the instructed offset amount from the offset amount storage means 13, and offsets the programmed path using the offset amount, thus generating a machining path along which a wire electrode 2 actually moves.
In wire electrical discharge machines, improving machining accuracy in a corner portion is an important theme. The shapes of corner portions formed by wire electrical discharge machining include various shapes formed by combinations of arcs, and right, acute and obtuse angles, and projections and depressions. Moreover, with regard to control methods, since characteristics are different between methods concerning rough machining and methods concerning finish machining, various control techniques have heretofore been proposed to improve machining accuracy in corner portions.
In a wire-cutting shape modification method for wire electrical discharge machining disclosed in Japanese Patent Application Laid-Open No. 59-115125, in the case where a machining path intersection of two blocks instructed in a basic program is an intersection to be subjected to concave portion machining, a machining path as a wire electrode travel path having the shape of an arc which has a center at the intersection and which has a radius equal to an offset value for a wire electrode with respect to a machining path is added to the above-described intersection portion.
In the above-described wire-cutting shape modification method, an arc-shaped machining path which has a center at the intersection of the blocks and which has a radius equal to the offset value is added to a workpiece side so that roundness occurring in a concave sharp corner portion, which causes a problem in die machining and the like, may be removed. A corner in which the machining path is compensated is a concave sharp corner, and a newly inserted machining path is located outside the corner. Accordingly, this technique is obviously different from the present invention.
In a wire electrical discharge machining method disclosed in Japanese Patent Application Laid-Open No. 4-217426, in a phase in which a rough cut and subsequent finish cuts are performed, a first cut is performed such that an arc portion in a cutting shape having a radius equal to or less than a preset reference radius is machined using a machining path obtained by inserting an arc which is tangent to machining paths before and after the arc portion and which has a radius smaller than a predetermined radius. In subsequent cuts, machining is performed while the machining path is being converted by gradually increasing the radius of respective arcs to be inserted in machining.
The above-described wire electrical discharge machining method is intended to improve the shape accuracy of a corner portion of an arc-shaped path in a machining program, and intended to reduce the amount of machining in finish cuts as much as possible by setting a machining path for a rough cut at a concave arc corner such that the machining path reaches as deep a position as possible in the corner. This technique exerts effects on the assumption that multiple finish cuts are performed, and the operation thereof is not to insert a path inside the concave arc. Accordingly, this technique is obviously different from the present invention.
In a shape compensation method for wire electrical discharge machining disclosed in Japanese Patent Application Laid-Open No. 57-114331, in the case where an arc-shaped cut is performed, the amount of tangential deflection and the amount of radial deflection are calculated, and a machining path is modified based on deflection amount components.
In the above-described shape compensation method, the amount of deflection during linear machining is measured in advance, and tangential deflection and radial deflection during an arc-shaped cut are calculated based on the measured amount to compensate a machining path. This method requires deflection measurement and has the problem that a dull corner or an overcut occurs if compensation amounts are not accurately calculated. Moreover, since the compensation of a machining path does not eliminate the deflection of a wire, there is also a problem that deviation from straightness accuracy with respect to the thickness direction of the workpiece is not eliminated. Further, the operation thereof is not to insert a path inside the concave arc. Accordingly, this technique is obviously different from the present invention.
In a controller and a machining path generator of a wire electrical discharge machine disclosed in Japanese Patent Application Laid-Open No. 2010-99824, in the case of a cutting shape including a concave sharp corner portion formed by two intersecting linear movement blocks which are not parallel to each other, a portion of the cutting shape on the concave sharp corner portion side is deleted, and a movement block for an arc shape having a set radius is inserted in the deleted portion.
The above-described machining path generator compensates a machining path by inserting an arc-shaped block in a concave sharp corner, thus preventing an increase in the amount of machining when multiple cuts are performed on the concave sharp corner portion, and improving machining accuracy. A corner in which the machining path is compensated is a concave sharp corner, and the operation thereof is to delete a portion of a linear block and newly insert an arc-shaped block. Accordingly, this technique is obviously different from the present invention.
In a controller of a wire electrical discharge machine disclosed in Japanese Patent Application Laid-Open No. 2008-260081, in the case of a cutting shape including a concave sharp corner portion formed by two intersecting linear movement blocks which are not parallel to each other, a portion of the cutting shape on the concave sharp corner portion side is deleted in each cutting pass after a set reference number of cutting passes, and a movement block for an arc shape having a radius of curvature determined based on an offset difference is inserted.
The above-described controller compensates a machining path by inserting a block for an arc shape in a concave sharp corner, thus preventing an increase in the cutting margin of a concave sharp corner portion, and improving machining accuracy. Similar to the aforementioned technique disclosed in Japanese Patent Application Laid-Open No. 2010-99824, a corner in which the machining path is compensated is a concave sharp corner, and the operation thereof is to delete a portion of a linear block and newly insert an arc-shaped block. Accordingly, this technique is obviously different from the present invention.